fa2 0.3.0

Rust implementation of the Force Atlas 2 graph layout algorithm.
Documentation 
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use crate::settings::FA2Settings;
use crate::traits::Float;

#[inline]
pub fn apply_nodewise_gravity<F: Float>(
    settings: &FA2Settings<F>,
    x: F,
    y: F,
    mass: F,
    out_x: &mut F,
    out_y: &mut F,
) {
    let g = settings.gravity / settings.scaling_ratio;

    let mut factor = F::zero();

    let distance = (x.powi(2) + y.powi(2)).sqrt();

    // TODO: make this branchless
    if distance > F::zero() {
        factor = settings.scaling_ratio * mass * g;

        // TODO: make this branchless
        if !settings.strong_gravity_mode {
            factor /= distance;
        }
    }

    *out_x -= x * factor;
    *out_y -= y * factor;
}

#[inline]
pub fn apply_gravity<F: Float>(
    settings: &FA2Settings<F>,
    xs: &[F],
    ys: &[F],
    ms: &[F],
    out_xs: &mut [F],
    out_ys: &mut [F],
) {
    for n in 0..xs.len() {
        let x = xs[n];
        let y = ys[n];
        let m = ms[n];

        apply_nodewise_gravity(settings, x, y, m, &mut out_xs[n], &mut out_ys[n]);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_apply_gravity() {
        let settings = FA2Settings::<f32>::default();

        let xs = [1.0, 2.0];
        let ys = [3.0, -5.0];
        let ms = [1.0, 1.5];
        let mut out_xs = [1.0, 2.0];
        let mut out_ys = [3.0, -5.0];

        apply_gravity(&settings, &xs, &ys, &ms, &mut out_xs, &mut out_ys);

        assert_eq!(out_xs, [0.6837722, 1.442914]);
        assert_eq!(out_ys, [2.0513167, -3.607285]);
    }
}